Driving Impressions: Super-Sized Hybrid

A few weeks before I had the opportunity to drive GM's vision of a fuel cell future, I spent some time behind the wheel of a piece of sophisticated technology that GM is already selling--the GMC Yukon hybrid.

The takeaway: The hybrid Yukon is quiet and handles well. For most folks, the truck is probably not worth the price premium it carries over the standard Yukon, not unless gasoline goes well north of $4 per gallon, as some analysts expect by this summer.

This is a truck, however, for people who want to be different, love new technology or do most of their driving in city conditions, where this vehicle is most efficient. And someday, going with a hybrid may be about the only way you can buy a 16-foot-long sport utility vehicle.

The Yukon features a new two-mode hybrid system, a technology that
General Motors
developed in partnership with BMW, Daimler and Chrysler. GM offers the same hybrid system of the Yukon's sister, the Chevrolet Tahoe, and this fall will start selling, on a limited basis, big pickup hybrids (Chevrolet Silverado and GMC Sierra).

At over two tons, the Yukon is at the opposite end of the hybrid spectrum from the
Toyota
Prius, and it is doubtful whether Yukon-like vehicles will ever meet the future 35-miles-per-gallon mandate.

Big trucks, however, are one of the most profitable segments of the auto business. Automakers will likely try to improve fuel economy of their trucks as much as possible, while offsetting their fleet economy figures with sales of smaller, higher-mileage vehicles. Like it or not, in the big truck segment of the market we will be seeing more hybrids, diesels and smaller motors.

So how does today's super-sized hybrid stack up? Let's start with ignition. Turn the key and you hear an initial rush of sound and vibration, akin to staring up a diesel engine. The vehicle immediately settles down into near-silence.

When you tap the gas pedal, it's clear the Yukon is no wimp; it has plenty of oomph for a vehicle its size. The standard two-wheel-drive Yukon weighs in at 5,270, the four-wheel-drive at 5,527. The hybrid versions weigh in at 5,617 pounds and 5,835 pounds for two-wheel drive and four-wheel-drive, respectively.

GM engineers need to work on refining two things. The hybrid's throttle has a bit of a motorcycle feel: As soon as you let off the gas, there is a noticeable letdown in acceleration, which is unusual for a vehicle with an automatic transmission.

The regenerative brakes on the Yukon are also a bit too grabby. The trade-off is that GM claims that the regenerative brakes in combination with the conventional brakes provide noticeably shorter braking distances and help extend the life of the conventional brake pads.

How about fuel economy? One way that the hybrid Yukon saves gas is with its stop-start gasoline motor, something that comes in quite handy on a stoplight-laden stretch of road or in bumper-to-bumper traffic. This vehicle, with a regular gasoline 6-liter, 332-horsepower V-8, delivers 21 miles city and 22 miles highway in two-wheel-drive models.

Compare this to city/highway miles per gallon of 14 and 20 for the 5.3-liter V-8 that is available in the standard two-wheel-drive Yukon. That amounts to 50% improvement in city driving and 10% highway. GM claims an overall 25% improvement in fuel economy. Towing capacity suffers, though. The hybrid can pull 6,200 pounds vs. 6,400 pounds or 7,400 pounds (depending on axle ratio) for the two-wheel-drive model with the 5.3-liter V-8 motor.

At the heart of the two-mode hybrid system is its sophisticated electronic variable transmission (EVT), which has both continuously variable components for low-load operations as well as four fixed gears for high-load operations. First mode is for low speed and light loads. Under these conditions, the vehicle operates on electric power only, engine power only or a combination of the two. In the first mode, the vehicle can accelerate up to 30 miles per hour on electric alone.

The second mode is for highway speeds, where it can use the electric assist for acceleration. In both modes, the V-8 gasoline motor can cut off four cylinders during cruising. The vehicle has a 300-volt nickel-medal-hydride battery pack, located under the rear seat, and has two 60-kilowatt electric motors integrated within the transmission. Only the electric motors propel the vehicle in reverse gear.

As is common with a continuously variable transmission, the noise under-hood and the acceleration of the vehicle are not always in synch. There is a bit of a growl, for example, in mid-range passing.

Beyond transmission, GM modified several items to make the hybrid more efficient than the standard vehicle. Front seats, for example, are thinner and lighter. The front and rear fascia of the Yukon hybrid are more aerodynamic, but the air dam is so close to the road that it pretty much rules out any off-road activities.

GM lopped off the roof rack too, in order to help reduce drag. And the liftgate is one piece, with fixed glass vs. a rear window that opens separately on the conventional model.

On the wheels, the hybrid has low resistance tires, but they are not run flats. Nor is there a spare tire, just a tire sealant and inflator kit. The standard Yukon comes with a full-sized spare.

But it's not all sacrifice for the hybrid. It has electric power steering, which GM claims provides a 0.5-miles-per-gallon gain. Also, the cylinder cutoff, available in the 5.3 V-8 conventional Yukon, is more efficient in the hybrid because it can get a 30-horsepower boost from the electric motors.

Including destination and two options (a rear-seat entertainment center and a sunroof), our two-wheel-drive tester had a total sticker of $53,235. It is hard to make an exact price comparison, as the Yukon hybrid is only available with standard luxury and convenience features such as a navigation system, leather seats and remote start. Figure on an invoice $7,000 higher for the hybrid over a two-wheel drive conventional Yukon with the 5.3-liter V-8 and similar equipment.

If you do shell out the extra seven grand here, you won't be an unhappy truck owner. GM's current-generation big SUVs--whether with a conventional motor or hybrid system--are quantum levels better than its previous models. The driving experience in the hybrid Yukon is different, but not objectionable.